The present invention relates to an image forming apparatus which forms an image on recording medium by ejecting liquid such as ink from a printing head, and a pump for such an image forming apparatus.
In an image forming apparatus such as an ink jet printer, ink is ejected from the ejection orifices of a printing head to form an image on a piece of recording medium. During the operation of such an image forming apparatus, ink (with increased viscosity), dust, and the like, adhere to the ejection orifices of the printing head. Thus, in order to remove these contaminants, an ink jet printer is generally provided with a recovery means to keep stable the ink ejection performance of the printer.
A recovery means generally comprises a capping means, a wiping means, and a pumping means. The capping means comprises a plurality of caps for covering the printing head, across the surface with ejection orifices, while the apparatus is not recording. It prevents ink from drying or evaporating while the apparatus is not recording. The wiping means comprises a blade or the like for removing the ink adhering to the printing head surface with ejection orifices. The pumping means suctions the ink with increased viscosity, and the like, from the ejection orifices and their adjacencies, through the capping means.
Generally speaking, a conventional pumping means comprises a cylinder and a piston which shuttles within the cylinder, with its peripheral surface remaining in contact with the internal surface of the cylinder. Technology regarding such a pumping means is disclosed in Japanese Laid-Open Patent Application No. 067,121/1998.
FIG. 18 is a schematic sectional drawing which presents an example of a conventional pumping means for an image forming apparatus. As depicted in FIG. 18, the pumping means comprises a cylinder 160, and a piston 164 which shuttles within the cylinder 160. The cylinder 160 is provided with two ink suction holes 161 and 162 and one ink discharge hole 163. The ink suction holes 161 and 162 are connected to two capping members (unillustrated), one for one.
When the pumping means structured as described above is in operation, the piston 164 shuttles within the internal space of the cylinder 160, with its peripheral surface remaining in contact with the internal surface of the cylinder 160. As the piston 164 shuttles, ink is suctioned into the cylinder 160 through the ink suction holes 161 and 162, and then is discharged from the cylinder 160 through the ink discharge hole 163 as a common ink discharge hole. This pumping means is superior in space utilization efficiency, compared to a pumping means which comprises two caps, and two cylinders parallelly disposed corresponding one for one to the two caps. In other words, this pumping means has an advantage over the latter, in that it makes it possible to reduce the overall size of an image forming apparatus.
However, the pumping means structured as described has a problem. That is, after the ink is suctioned into the cylinder, the ink is left alone to discharge itself out of the cylinder by its own weight. As a result, a certain amount of ink remains within the cylinder. If the ink which is remaining in the cylinder adheres to the internal surface of the cylinder and solidifies there, there is a possibility that the gap between the cylinder and piston fails to be properly sealed. If the gap fails to be properly sealed, air is allowed to leak through the gap, causing the pumping means to fail to properly suction ink. There is also a possibility that the ink will remain between the cylinder and piston and solidifies there. If the ink which is remaining between the cylinder and piston solidifies, the force required to make the piston slide on the internal surface of the cylinder sometimes becomes large enough to prevent the piston from being driven, which results in ink suction failure.
A principal object of the present invention is to provide an image forming apparatus pump which does not suffer from leakage and waste liquid solidification which lead to suction failure, and to provide an image forming apparatus equipped with such a pump.
Another object of the present invention is to provide an image forming apparatus pump capable of easily discharging waste liquid, and to provide an image forming apparatus equipped with such a pump.
According to an aspect of the present invention, there is provided an image forming apparatus comprising cap members for capping ejection outlets of an ejection portions for ejecting liquid to a recording material; pump means including suction inlets in fluid communication within said cap members; discharging outlets for discharging the liquid; cylinder means including a plurality of cylinders having said suction inlets and said discharging outlets, respectively; a seal member for dividing inner space in the cylinder means into said cylinders; and a plurality of pistons reciprocable in the spaces in contact with the inner surfaces of the cylinders to produce pressure change in the inner spaces; wherein in each of said cylinders, said suction inlet is disposed more away from seal member than said discharging outlet.
According to another aspect of the present invention, there is provided a pump for an image forming apparatus which includes cap members for capping ejection outlets of an ejection portions for ejecting liquid to a recording material, said pump comprising suction inlets in fluid communication within said cap members; discharging outlets for discharging the liquid; cylinder means including a plurality of cylinders having said suction inlets and said discharging outlets, respectively; a seal member for dividing inner space in the cylinder means into said cylinders; and a plurality of pistons reciprocable in the spaces in contact with the inner surfaces of the cylinders to produce pressure change in the inner spaces; wherein in each of said cylinders, said suction inlet is disposed more away from seal member than said discharging outlet.
As described above, according to the present invention, an image forming apparatus pump comprises a plurality of cylindrical portions which are provided with the suction hole or holes and discharge hole or holes, and are aligned in a straight line; a single or plural sealing members which serve as a divider between the internal spaces of the adjacent two cylinder portions, and a plurality of pistons which shuttle within the correspondent cylinder portions, with the peripheral surface thereof remaining in contact with the internal surfaces of the cylinder portions, to change the internal pressures of the cylinder portions. After being suctioned into the internal spaces of the plurality of cylinder portions, liquid is almost completely discharged through the discharge holes by the pressure generated in the space between the pistons and correspondent sealing members. In other words, according to the present invention, it is possible to prevent leakage and solidification of waste liquid, which lead to suction failure, by reducing the amount of the liquid which remains in the cylinder.
Further, the present invention eliminates the need for arranging a plurality of the cylinder portions in parallel corresponding to a plurality of capping member, making it possible to reduce the overall size and cost of an image forming apparatus.
Further, according to the present invention, in each cylinder portion, the suction hole is disposed on the far side, with respect to the discharge hole, from the sealing member, making it possible to place the discharge holes closer to each other to make it easier to dispose waste liquid.
Further, according to the present invention, a plurality of rings are on the peripheral surface of each of the plurality of pistons so that only the peripheral surfaces of the rings make contact with the internal surface of each cylinder portion, reducing the size of the contact area between the internal surface of the cylinder and the peripheral surface of the piston. Therefore, even if liquid enters between the internal surface of a cylinder portion and a piston, and solidifies there, it does not occur that liquid fails to be satisfactorily suctioned due to the insufficiency in the piston driving force.
Further, according to the present invention, among the plurality of the rings on the peripheral surface of each of the plurality of pistons, the ring on the upstream side in terms of the direction in which the piston moves for suctioning is rendered greater in external diameter than the ring on the downstream side, equalizing both rings in their contact pressure upon the internal surface of the cylinder portion to prevent leakage. Therefore, liquid is reliably suctioned.
In addition, the force required to drive the pistons is smaller, making it possible to employ a motor, or the like, with relatively low torque as a driving force source to reduce noise level compared to when a high torque motor is employed.
These and other objects, features, and advantages of the present invention will become more apparent upon consideration of the following description of the preferred embodiments of the present invention, taken in conjunction with the accompanying drawings.